The invention relates to functional devices and their attachment to textile or other substrate material, as for example snap fasteners for articles of clothing, disposable garments, and the like.
Conventional methods of attaching a functional part to a substrate or foundation material usually involve the two separate steps of (a) fabricating the functional part as a discrete item, and (b) attaching the functional part to the substrate or foundation material. Attachment can utilize a surface effect, as via an adhesive, welding, brazing, and soldering; or the substrate can be pierced to accommodate threaded, riveted or swaged projections, or the like.
The invention is regarded as applicable to a wide variety of functional-attachment situations but to simplify present description, the context of use of the invention will primarily concern "snap fasteners", employed as detachable closure devices in the apparel industry. Such snap fasteners have come in many varieties, but they are illustrative of conventional practice requiring prefabrication of discrete parts, usually of steel, brass, or plastic resin, the same being attached to fabric by piercing and joining to a companion part, or "cap".
Current technology involves the fabrication of snap fasteners as a separate operation, in a first industry or manufacturing facility; the fabricated fastener parts are supplied to another industry or manufacturing facility where fastener parts are manipulated in relation to a fabric and are then attached to the fabric. A typical fastener consists of a "set" of four parts, as shown in FIG. 1, namely, as indicated by legend, stud and socket parts which are separably engageable by snap fit, and a cap part for securing each of the stud and socket parts to its particular garment region. When the four-part fastener is of molded plastic, the snap action of separable engagement is occasioned by compliantly yielding interference as the bulbous stud traverses the entrance to the hollow of the socket; when such a fastener is of metal, the yielding interference is realized by segmenting the socket geometry into individual spring fingers, or by the use of wire rings or other compliantly deformable shapes.
The operative stud and socket parts of FIG. 1 are shown securable to fabric via cap prongs which pierce the fabric, but this is but one of various fabric-piercing cap techniques which are conventional, for example, metal caps with projecting eyelet, prong-cage or staple formations, or molded-plastic caps with projecting post or prong formations. In every case, four parts must be separately fabricated, the fabric must be pierced, and an upsetting, curling or swaging operation is needed to clinch the cap and operative fastener part so as to sandwich its fabric foundation.
Quality of attachment is of key importance in producing a satisfactory fastener, and most development work in the industry has been directed toward obtaining more secure attachment to the substrate; for example, it is a common practice to fold the fabric into several layers of thickness, with insertion of one or more layers of reinforcing material, to provide better integrity for the sandwiched cap-secured stud or socket part. But with repeated engagement/disengagement cycling of the fastener, lateral forces tend to pull or tear the fabric through the "sandwich". Tightly woven cotton and blend fabrics are more resistant to tear, while synthetic knits and solid sheets are more readily damaged. Metal snaps can be tightly clinched to create a clamping action, or "pinch", on the fabric. But a pinching clamp is not readily achievable with plastic fastener parts, due to inherent resilience of the plastic material.
The need for four parts in a snap-fastener "set" has created an aesthetic requirement. The industry has decorated the non-functional parts (i.e., caps) with designs and geometries to enhance appearance on the face side of the garment. In some cases, design orientation is important, thus dictating another positional or orientation requirement.
The attachment of snap fasteners requires special machinery, which varies in complexity, from simple foot-operated presses to electrically or pneumatically driven units which automatically feed, orient and attach a stud or socket part to its companion cap, eyelet, staple or prong. The operator inserts and locates the garment and triggers the machine, which feeds the active part on one side, the inactive part on the other, and clinches them together. Further sophistication involves feeding the garment through the machine automatically, and attaching multiple snaps. These machines are usually leased to the user on an annual basis, and must be serviced by trained mechanics. Attaching machines now on the market are not readily converted to other sizes or types of fasteners. In many cases, a seasonal garment requirement calls for short use and is then left idle, while the leasing cost continues.
Cost is a primary factor for relevant comparison of the present invention. Typical four-part metal snap fasteners range in price from $40.00 to $100.00 per thousand sets, and plastic fasteners range from $15.00 to $50.00 per thousand sets.
The current market for snap fasteners is believed to be in the order of $100 million annually in the United States, and to several times this figure worldwide, it being understood that these figures include cost of the products as well as leasing costs of the machines to assemble them. The major application is to apparel; other and lesser applications include footwear, tarpaulins, luggage, envelopes, and appliance and machine panels.